1. Field of the Invention
The present invention relates to a coherent mixer and a 2×2 multi-mode interference (MMI) coupler.
2. Description of the Related Art
R. Kunkel, H-G. Bach, D. Hoffmann, and C. M. Weinert, “First monolithic InP-based 90°-hybrid OEIC comprising balanced detectors for 100GE coherent frontends”, IPRM2009, TuB2.2, IEEE discloses an integrated device on which a 90 degree hybrid (90 deg hybrid) and a photodiode are monolithically integrated.